Control of electric arcs used in welding or metal spraying processes



July 21, 1953 w. E. BALLARD 2,646,492

CONTROL OF ELECTRIC ARCS USED IN WELDING 0R METAL SPRAYING PROCESSES Filed July 8, 1950 Patented July 21, 1953 UNITED CONTROL OF ELECTRIC ARCS USED IN WELDING OR METAL SPRAYING PROCESSES William Edward Ballard, Harborne, Birmingham, England Application July 8, 1950, Serial No. 172,638 In Great Britain July 13, 1949 3 Claims.

This invention relates to the control of electric arcs used in processes in which an arc is formed for fusing or melting metal, such as welding and metal spraying processes.

In such processes as electric welding and metal spraying by means of an electric are many of the difiiculties encountered are due to the fact that the arc is easily broken due partially to the high resistance offered by the gaseous path. For instance difiiculties are encountered in those processes of welding or metal spraying in which an electrode is advanced towards another stationary electrode of metallic or non-metallic material, or in those cases where. such electrodes advance together towards a common point and an arc is established between the advancing electrodeand its counterpart, the latter arc being used to melt said electrodes themselves, or a wire fed in to the arc mechanically.

To overcome these difficulties, it has been proposed that the gaseous path of the arc should be ionised, and various methods have been suggested, such as the superimposition on the main current of a high-frequency discharge. Most of the methods which have been proposed have the disadvantages that they require a considerable amount of electrical apparatus, and that they are not altogether satisfactory in working.

With the object of overcoming or reducing these difiiculties, I provide in an apparatus for the deposition of molten metal or" the kind comprising a chamber having inlet port for gas and a discharge orifice for the gas, electrode supporting means and at least one electrode supported thereby having an arc-forming extremity positioned in the locality of said orifice; a body of radioactive material supported within said chamber in the path of gas passing through said chamber between said inlet and said orifice and at a distance from said electrode extremity corre sponding to the ion-pair forming range of said material.

The radioactive material may be either in the form of a naturally occurring element, e. g., plonium, or in the form of a radioactive isotope such as may be manufactured in an atomic pile The position of the radioactive material in relation to that of the arc is important. The radioactive source is spaced away from the arc path by a distance which depends upon the nature of the source being used.

The different types of radioactive material ive emanations of different energies, and the ionisation produced is largely dependent on providing the optimum path for production of ion pairs; thus :when using polonium providing alpha ray emissions a distance of approximately 3 ems. in air is adequate; whereas the beta emissions from phosphorous 32 requires approximately 8 cms. If the distance is too large recombination of ion pairs takes place, and. obviously it is desirable to mount the radioactive source so that the minimum of radiation is absorbed by the materials of construction of the welding or metal spraying unit.

The following examples of how the invention may be carried into efiect are given for guidance only and do not preclude other arrangements of the arc and the radioactive source to bring about similar ionisation.

These examples are illustrated in the accompanying drawing, wherein:

Figure 1 is a diagram showing the application of the invention to a Welding process; and

Figure 2 is a diagram showing the application of the invention to a metal spraying process.

The inert arc welding torch is a well-known piece of apparatus in which a tungsten electrode is surrounded by a shroud of inert gas flowing at the rate of about 7 litres per minute. The other electrode is the work to be welded, and a filler rod may be melted in the name of the are so formed. The gas is usually fed to the arcing point through a nozzle which is generally so arranged as to give an annular space around the electrode.

In carrying my invention into effect as shown in Figure 1, an inert gas is fed through a tube In to a chamber II, which may terminate in a nozzle I2. One electrode [3 is disposed centrally in the chamber H, and also mounted in the chamber H is a member I4 which may consist of a plate carrying radioactive material, or which may be made of radioactive material. This source of radioactive emissions is spaced away from the end [5 of the electrode [3 by a distance which varies according to the kind of radioactive material used; for polonium the distance may be approximately 3 cms. The are produced is used for welding the work l6, and a filler rod may a be melted in the flame of the are if desired. The second electrode is formed by the work i5.

It will be observed that in the diagram the end of the electrode 55 projects from the nozzle l2, and the inert gas passing through the charm her I! is discharged in a screen around the end or" the electrode. If the radioactive material is phosphorous 32, the distance between the radioactive material and the end of the electrode is greater and may be about 8 ems.

Metal spraying tools are well known which en body two mechani ally-driven wires which approach one another through Wire guides at a predetermined angle, and in applying the present invention to such a tool the radioactive source i? is fixed on a suitable mount between the wire guides 18, being in such a position that the maximum ionisation of the gas passing the are at E9 is achieved, together with the minimum recombination of ion pairs. In efiect the tube or chamber 20 terminating in the nozzle 2! becomes an ionisation chamber in which the propellant gas fed in at 22 is ionised, and the size and shape of this chamber are critical and depend on the nature of the radioactive source. W 3 instance in using polonium the source is mounted on a base as permeable as possible to the alpha radiations, and at a distance from the surrounding walls and are as near as possible to 3.5 ems. when air is bein used.

The wires are caused to be the electrodes, and in the case of an alternating current circuit the open circuit voltage may be approximately 89 volts. When an arc is struck between the advancing electrodes, the voltage falls to about 30 and the amperage may be in the order or" The presence of gases ionised by the radioactive material have aconsiderable smoothing effect on the arcing circuit.

In the present invention low voltage high amperage current is used. The voltage may be up to 230 volts and the current is not less than 5 amperes and will usually be very considerably in excess of this.

The radioactive material may be a naturally occurring radioactive material, such for instance as radium, thorium or polonium, or the radioactive material may be an unstable radioactive isotope, such as radio-phosphorous or radio-cobalt, either elemental or combined, manufactured by means of the atomic pile or the cyclotron. Further, the radioactive material employed may be a combination of naturally occurring radioactive material and manufactured radioactive material.

What I claim then is:

1. In an apparatus for the deposition of molten metal of the kind comprising av chamber having an inlet port for gas and a discharge orifice for the gas, electrode-supporting means, and at least one electrode supported thereby having an arctrode supported thereby having an arc-torn extremity positioned in the locality of said orifice outwardly of said chamber; the provision of a body of radioactive material supported within said chamber in the path of gas passing through said chamber between said inlet and said orifice and at a distance from said electrode extremity corresponding to the ion-pair forming ran e of said material.

3. In metal spraying apparatus of the hind comprising a chamber having an inlet port 10 gas and a discharge orifice for he as, electrode supporting means, a pair of electro; thereby, said electrodes having spas .i but adjacent arc-forming extremities positioned within said chamber in the locality of said orifice; the provision of a body of radioactive material supported within said chamber in the path or gas passing through said chamber between said inlet and said orifice and at a distance from said electrode extremities corresponding to the ion-pair forming range of said material.

'WILLIAM ED'W BALLARD.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Ser. No. 376,930, Peycelon et al. (A. (3.), published May 25, 1943. 

